a. Field of the Invention
This invention relates to a thin-film high recording density magnetic recording medium having a magnetic layer formed by sputtering, vapor deposition or vacuum evaporation, or plating, and, more particularly, to a magnetic recording medium wherein a protective layer resistant to sliding friction with magnetic heads is formed to extend the life thereof.
b. Prior Arts
For magnetic recording media such as magnetic disk or magnetic tape, it is important to reduce the problem of abrasion of the medium due to the sliding motion between a magnetic head and the medium. Especially, a thin-film magnetic recording medium in which a magnetic layer is directly formed by sputtering, vapor deposition or vacuum evaporation, or plating does not allow for the step of mixing a lubricant into a binder as opposed to conventional media wherein a magnetic layer is formed by dispersing ferromagnetic powder in a binder and coating the composition followed by drying. For this reason, the problem is more difficult to solve in the former case.
In order to improve the resistance of the thin-film magnetic recording medium to abrasion and wear due to sliding friction, it is desirable to provide a lubricating protective layer on the surface of the magnetic layer. There have been proposed various methods for forming a lubricating protective layer. These methods are, for example, by coating a liquid lubricating oil, sputtering an organic polymer to form a thin film (Japanese Patent Application Kokai No. 57-116771), polymerizing a fluoro organic compound or an organic silicon compound in a plasma for deposition (Japanese Patent Application Kokai No. 51-127702), vacuum depositing a higher fatty acid (Japanese Patent Application Kokai No. 54-11303), and sputtering carbon to form a thin film (Tago et al., The 8th Applied Magnetism Society of Japan's Scientific Conference Papers, p. 222, Nov., 1984). The present inventors have followed these methods to find that the life of the resultant media is extended as compared with protective layer-free media, but not to a sufficient extent for actual use. However, it has been found that sputtered carbon films have a low coefficient of abrasion and are difficult to wear out. The sputtered carbon films, however, are not fully effective as such because they weakly adhere to the magnetic layer and are readily peeled off by the sliding friction.